Formation energy, mechanical and electronic properties of buckled heptazine (C6N8) sheet: First-principles calculations

Abstract Using first-principles calculations based on density functional theory (DFT) the formation energy ( E FE ), elastic constants, elasticity and electronic property of buckled C 6 N 8 sheet are examined. The calculated negative E FE (-0.34 eV) confirms the experimental synthesis of the buckled C 6 N 8 sheet. It is revealed that the obtained in-plane stiffness ( Y x / Y y ) along the x (90.48 N/m) and y - (100.25 N/m) are lower than that of planar heptazine (212.46 N/m) and striazine (133.55 N/m) sheets. The decrease in rigidity is mainly due to the bonding nature of the sheet causing softening for the buckled hexagonal rings and hardening for the planar rings. The calculated Poisson's ratio ( v x / v y ) is 0.166/0.183 which is larger than that reported planar heptazine (0.10) and striazine (0.08) sheets. The bulk modulus (57.8 N/m) of buckled C 6 N 8 sheet is about half the value to that of planar heptazine sheet (108.01 N/m). The estimated values of the critical strains (elastic and yielding) points show that the buckled C 6 N 8 sheet cannot withstand larger tensions as compared with the planar heptazine sheet. These results established a stable mechanical property for the buckled C 6 N 8 sheet. Also the buckled C 6 N 8 sheet exhibits intrinsic semiconducting property with an indirect band gap of 1.85 eV. These noble properties can be useful in carbon-based nanosheet applications.